Electrical switches are used for switching electrical currents. One class of electrical switches is the so-called power switches (line circuit breakers), which can typically switch currents of more than 100 A. Line circuit breakers are typically accommodated in a housing. The individual phases of the current are typically switched in so-called pole cassettes. Pole cassettes are housings in which are accommodated a movable and a fixed contact, which can be mechanically separated or brought together for the purpose of switching the currents off or on respectively. The mechanisms for activating the switching off and on of the individual pole cassettes are put together in such a way that they can be switched using a single handle at the electrical switch.
In addition to the function of switching the electric current on or off, as appropriate, the housing for an electrical switch often accommodates an electronic trip unit (ETU). An electronic trip unit has the task of analyzing a current signal received from the electrical switch, for example in respect of short circuits or overcurrents. As soon as it detects a short circuit or an overcurrent, the electronic trip unit trips the electrical switch, which means that the switch is switched off, in that the contacts are separated and the current flow is thereby interrupted.
In many applications, the electronic trip unit is linked with other electrical devices for further processing of its input or output signals. These other electrical devices could be, for example, a residual current device (RCD) or an external N-conductor converter. These are typically linked to the electronic trip unit by means of a cable connection, where the electronic trip unit itself interoperates with the electrical switch through contacts in the latter's housing. The connections for the other electrical devices are typically located on the operating area of the electronic trip unit, where they can be accessed after removal of a cover. Equally, the connections for the other electrical devices can be located in a so-called accessory holder on the switch. Accessory holder is the term used for a space in the housing of an electrical switch which, in the built-in position, is located alongside the handle, while the electronic trip unit is typically arranged above or below the handle.
Typically, the electrical switches described above will be built into a switchgear cabinet. This is provided with a door to prevent unauthorized operation of the switches and other built in items. For reasons of space, there is often not much room available between the surface of the electrical switch and the door. If the connections for the other electrical devices are now located on the operating area of the electronic trip unit, or in an accessory holder, it is often only with difficulty possible to close the door of the switchgear cabinet, or switchgear cabinets with a greater installation depth are required, as applicable.